[PATCH] Add function entry count metadata.

[David Blaikie]

On Sat, May 9, 2015 at 3:56 PM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Fri, May 8, 2015 at 4:04 PM, Diego Novillo <dnovillo at google.com> wrote:
>
>> Hi dexonsmith, bogner,
>>
>> This adds three Function methods to handle function entry counts:
>> setEntryCount(), hasEntryCount() and getEntryCount().
>>
>> Entry counts are stored under the MD_prof metadata node with the name
>> "function_entry_count". They are unsigned 64 bit values set by profilers
>> (instrumentation and sample profiler changes coming up).
>>
>> I had some internal debate about what to return when
>> Function::getEntryCount() is called without the function having its
>> metadata set. I don't want to return a special sentinel value, because
>> those are typically problematic down the road.
>>
>
> What sort of problems?
>
>
>> So, I added a Function::hasEntryCount() predicate. If
>> Function::getEntryCount() is called with no metadata present, it will
>> cause a compiler assertion.
>>
>
> If any caller would need to call hasEntryCount before getEntryCount,
> perhaps have getEntryCount return Optional<uint64_t> (& returns 'None' when
> not present)?
>

Heh - don't mind me - seems I should've read the replies made before I got
to this.


>
>
>>
>> http://reviews.llvm.org/D9628
>>
>> Files:
>>   include/llvm/IR/Function.h
>>   include/llvm/IR/MDBuilder.h
>>   lib/IR/MDBuilder.cpp
>>   unittests/IR/MetadataTest.cpp
>>
>> Index: include/llvm/IR/Function.h
>> ===================================================================
>> --- include/llvm/IR/Function.h
>> +++ include/llvm/IR/Function.h
>> @@ -23,7 +23,11 @@
>>  #include "llvm/IR/Attributes.h"
>>  #include "llvm/IR/BasicBlock.h"
>>  #include "llvm/IR/CallingConv.h"
>> +#include "llvm/IR/Constants.h"
>>  #include "llvm/IR/GlobalObject.h"
>> +#include "llvm/IR/LLVMContext.h"
>> +#include "llvm/IR/MDBuilder.h"
>> +#include "llvm/IR/Metadata.h"
>>  #include "llvm/Support/Compiler.h"
>>
>>  namespace llvm {
>> @@ -194,6 +198,29 @@
>>                                   AttributeSet::FunctionIndex, Kind,
>> Value));
>>    }
>>
>> +  /// @brief Set the entry count for this function.
>> +  void setEntryCount(uint64_t Count) {
>> +    MDBuilder MDB(getContext());
>> +    setMetadata(LLVMContext::MD_prof,
>> MDB.createFunctionEntryCount(Count));
>> +  }
>> +
>> +  /// @brief Return true if the function has a known entry count.
>> +  bool hasEntryCount() const {
>> +    MDNode *MD = getMetadata(LLVMContext::MD_prof);
>> +    if (MD && MD->getOperand(0))
>> +      if (MDString* MDS = dyn_cast<MDString>(MD->getOperand(0)))
>> +        return MDS->getString().equals("function_entry_count");
>> +    return false;
>> +  }
>> +
>> +  /// @brief Get the entry count for this function.
>> +  uint64_t getEntryCount() const {
>> +    assert(hasEntryCount() && "No entry count available for this
>> function");
>> +    MDNode *MD = getMetadata(LLVMContext::MD_prof);
>> +    ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(1));
>> +    return CI->getValue().getZExtValue();
>> +  }
>> +
>>    /// @brief Return true if the function has the attribute.
>>    bool hasFnAttribute(Attribute::AttrKind Kind) const {
>>      return AttributeSets.hasAttribute(AttributeSet::FunctionIndex, Kind);
>> Index: include/llvm/IR/MDBuilder.h
>> ===================================================================
>> --- include/llvm/IR/MDBuilder.h
>> +++ include/llvm/IR/MDBuilder.h
>> @@ -60,6 +60,9 @@
>>    /// \brief Return metadata containing a number of branch weights.
>>    MDNode *createBranchWeights(ArrayRef<uint32_t> Weights);
>>
>> +  /// \brief Return metadata containing the entry count for a function.
>> +  MDNode *createFunctionEntryCount(uint64_t Count);
>> +
>>
>>  //===------------------------------------------------------------------===//
>>    // Range metadata.
>>
>>  //===------------------------------------------------------------------===//
>> Index: lib/IR/MDBuilder.cpp
>> ===================================================================
>> --- lib/IR/MDBuilder.cpp
>> +++ lib/IR/MDBuilder.cpp
>> @@ -53,6 +53,16 @@
>>    return MDNode::get(Context, Vals);
>>  }
>>
>> +MDNode *MDBuilder::createFunctionEntryCount(uint64_t Count) {
>> +  SmallVector<Metadata *, 2> Vals(2);
>> +  Vals[0] = createString("function_entry_count");
>> +
>> +  Type *Int64Ty = Type::getInt64Ty(Context);
>> +  Vals[1] = createConstant(ConstantInt::get(Int64Ty, Count));
>> +
>> +  return MDNode::get(Context, Vals);
>> +}
>> +
>>  MDNode *MDBuilder::createRange(const APInt &Lo, const APInt &Hi) {
>>    assert(Lo.getBitWidth() == Hi.getBitWidth() && "Mismatched
>> bitwidths!");
>>
>> Index: unittests/IR/MetadataTest.cpp
>> ===================================================================
>> --- unittests/IR/MetadataTest.cpp
>> +++ unittests/IR/MetadataTest.cpp
>> @@ -2272,4 +2272,12 @@
>>    EXPECT_FALSE(verifyFunction(*F));
>>  }
>>
>> +TEST_F(FunctionAttachmentTest, EntryCount) {
>> +  Function *F = getFunction("foo");
>> +  EXPECT_FALSE(F->hasEntryCount());
>> +  F->setEntryCount(12304);
>> +  EXPECT_TRUE(F->hasEntryCount());
>> +  EXPECT_EQ(12304u, F->getEntryCount());
>> +}
>> +
>>  }
>>
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>>
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>
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